1. FIELD OF THE INVENTION
The present invention relates to an alternator for automobiles, and more particularly to a cooling device for cooling the stator winding, rectifier diode, etc. incorporated in the alternator.
2. DESCRIPTION OF THE RELATED ART
In the heretofore alternator for automobiles, it has been common in design that to achieve reduction in size or compactness and a higher output, the alternator incorporates in it a cooling device for cooling necessary parts such as the stator winding, rectifier diode, etc. In the cooling device of the kind specified above, as typically disclosed in, for example, Japanese Unexamined patent publication No. 148640/83, it is usually constructed that there are provided cooling fans on opposed sides of the rotor, one of which cooling fans being adapted to draw cooling air from outside into the alternator through the front bracket so as to cool the stator winding while the other being adapted to effect the same through the rear bracket so as to cool the rectifier diode mounted within the rear bracket and the stator winding as well.
With the conventional cooling device, in this concern, it has been common in design that either both of the two cooling fans have the same level of fan capacity (suction capacity), or the cooling fan on the front bracket side be selected as of a suction capacity smaller than that of the other cooling fan on the rear bracket side because the space available in the front bracket being rather restricted with a view to reduce the whole length of the alternator assembly. Under these design requirements, however, the situation may result that the negative pressure occurring in the suction sections of the respective cooling fans in the brackets side will surpass that in the front bracket. In consequence, the rectifier diode mounted on the rear bracket side is cooled virtually solely by the cooling air draft provided by the cooling fan on the rear bracket side (hereinafter shortly referred to as "diode-side fan").
Furthermore, it is difficult, in the case of the cooling fans being equal in capacity, to attain desired cooling of the exciting winding on the rotor because there will be no occurrence of cooling air draft (in an axial flow) flowing through the space in which the rotor is disposed. Still further, in cases where the diode-side fan is of a capacity greater than that of the cooling fan on the front bracket side (hereinafter shortly referred to as "opp. diode-side fan"), the diode-side fan develops in its suction section a greater negative pressure. As a result of this negative pressure differential, part of the cooling air draft through the opp. diode-side fan will flow toward the diode-side fan in the form of an axial flow. Since, however, the axial flow occuring in this occasion is directed aganist the flow of cooling air draft provided by the diode-side fan, there will be a reduction in the effective volume of cooling air that can be contributory to the cooling of the rectifier diode, hence resulting in lowering of the efficiency of cooling the diode.